QUESTIONS

(OBQ11.2)
A 35 year-old female presents after prolonged extrication from a motor vehicle collision complaining of severe pelvic pain. Physical examination reveals diminished perianal sensation. She is otherwise neurologically intact. Figures A through D are radiographs and representative CT cuts of her injury. Which of the following nerve roots has likely been injured? Review Topic

The clinical scenario is consistent with a high-energy sacral fracture. The radiographs in figures A and B demonstrate a sacral fracture with posterior displacement of the right hemipelvis seen on the inlet view. Figures C and D are axial and sagittal CT images which show a displaced fracture of the right hemisacrum along with a transvere fracture component through the S3 body . Diminished perianal sensation is concerning for an S2 nerve root injury.

Mehta et al reviewed the current management of sacral fractures. They note that the S1 and S2 nerve roots are more likely to be injured with sacral fractures as they occupy 1/3 to 1/4 of the neural foramina, as opposed to S3 and S4, which only occupy 1/6 of the neural foramina.

Robles reviewed the current literature to ascertain principles of evaluation and treatment for transverse sacral fractures. The author notes that injury to nerve roots S2 to S5 is manifested by impairment of urinary and anal continence and sexual function.

The first illustration demonstrates the sacral nerve root dermatomal distribution. The second shows a pelvic cadaver dissection demonstrating the sacral nerve roots as they exit the foramina.

(OBQ11.35)
A 20-year-old patient presents after jumping from the window of a burning building with a sacral fracture. Which of the following fracture patterns seen in Figures A through E would give this patient the highest risk of associated nerve injury?Review Topic

Answering this question relies on knowledge of the Denis classification of sacral fractures and their associated risks of nerve injury. Figure A represents a Denis Zone 3 (medial to the foramina) sacral fracture, which has the highest associated risk of nerve injury.

Denis et al outlined a novel classification system of sacral fractures based on the position of the fracture line relative to the sacral foramina. The authors found a 56.7% incidence of nerve injury in fractures that extended medial to the sacral foramina (zone 3), compared with 28.4% for fractures through the foramina (zone 2), and 5.9% for fractures lateral to the foramina (zone 1).

Mehta et al reviewed the current principles for management of sacral fractures. They note that bowel, bladder and sexual dysfunction occur in 76% of patients with zone 3 sacral fractures.

Illustration A below demonstrates the Denis classification of sacral fractures.